Equilibrium and stability of phase-separating Au–Pt nanoparticles

✍ Scribed by Nadi Braidy; Gary R. Purdy; Gianluigi A. Botton

• Publisher: Elsevier Science
• Year: 2008
• Tongue: English
• Weight: 725 KB
• Volume: 56
• Category: Article
• ISSN: 1359-6454
• DOI: 10.1016/j.actamat.2008.08.024

✦ Synopsis

We report on a theoretical and experimental investigation of Au-Pt nanoparticles (NPs). The Au-Pt miscibility gap is theoretically reevaluated for NPs of various sizes. The model includes a composition-dependent surface energy evaluated by considering surface segregation. Using precise quantitative energy-dispersive X-ray spectroscopy (EDXS) and high-resolution electron microscopy (HREM), the structural evolution of $20 nm Au(core)-Pt(shell) NPs upon annealing at various temperatures (300-800 °C) is studied. At low temperatures, only interdiffusion occurs between the core and the shell, while above $600 °C, the NPs evolve into Au-and Pt-rich crystals, separated by an interface. At these temperatures, the Au solubility in the Pt-rich phase is found to be 5-10% higher than the bulk phase diagram and agrees qualitatively with the theoretical model. Based on the EDXS and HREM results, the nature of the interface separating the Au-and Pt-rich phases within a NP is discussed and an estimate of its energy is obtained.